The present invention relates to a toggle assembly designed for vehicles or cars, which comprises a relay cylinder mounted on an end plate including a booster cylinder and an output cylinder, a control chamber mounted coaxially on the relay cylinder, a control valve arranged in operable association with the control chamber for regulation of a gas by a hydraulic pressure of a master cylinder, and a booster piston received in the booster cylinder and in operable association with the gas thus controlled.
In the prior art toggle device of the type as mentioned just above, a compressed air conduit for establishing communication between the control chamber and the back chamber of the booster cylinder for the booster piston is provided independently of the booster body. This conduit is connected to the control chamber by fixing it to a relay valve body through a O-ring by means of a suitable joint (bush), and is connected to the back chamber for the booster piston by welding it to the booster shell. In such an arrangement, compressed air at a pressure of 6 to 10 kg/cm.sup.2 is admitted into the control chamber, and is then fed into the back chamber for the booster piston via the compressed air conduit. This offered problems such as a lowering of the sealing property and air leakage. The booster shell made by press-molding has also been found to be inferior in the tolerance of the internal dimension to the aluminium body made by casting; this has an adverse influence on the service life or durablility of an annular rubber seal positioned on the outer sliding surface of the booster piston.
In order to lubricate the outer sliding surface of the booster piston including the annular rubber seal, a lubricating oil is applied thereon during the assembling of the booster piston. As the piston is repeatedly reciprocated, however, the coated lubricating oil is often caused to collect on both ends of the outer sliding surface, so that the surface is not satisfactorily lubricated. As a result, the annular seal is spoiled to such an extent that the air-tightness maintained thereby is destroyed. This further leads to unsatisfactory operation of the master cylinder. In order to cope with these problems, an additional amount of the lubricating oil is made up for through a supply hole formed in the cylinder. In the case of an air cylinder of the type wherein the booster piston is horizontally reciprocated, however, the lubricating oil thus supplied collects merely in the lower portion of the cylinder and does not sufficiently reach the upper portion thereof. Thus, the above-mentioned problems remain still unsolved.
In the prior art arrangement, an air cleaner is provided at an exhaust port for discharging an off-gas such as waste compressed air into the relay valve body with a view to preventing dust, water and so on from entering the assembly. The air cleaner so far used includes a collar having therein an exhaust port and mounted on the upper end of a connector, a cap-shaped cover having its open end bent and fixed with respect to the collar, and a filter disposed within the cover. In such an arrangement, however, the exhaust port is readily clogged by mud etc. Especially in the case of a large-sized vehicle or car, the booster body is mounted on the underside of the car body while being open to the view, so that water and dust flung up by the front wheels enter the exhaust port and cause easy clogging of the filter. Under such a situation, it is impossible to discharge the compressed air from the front chamber of the booster cylinder. In addition, the inoperativeness of the booster then interrupts the operation of the clutch or increases the force necessary for working the brake pedal. Thus, the prior art air cleaner offers a serious problem in view of safety.
A water- and dust-proof boot is usually interposed between the output cylinder body and the output rod. As such a boot, a bellows has widely been used which is designed to extend and contract in response to the movement of the output push rod. The bellows is provided therein with a ventilation hole for preventing abnormal deformation or destruction thereof during the extension and contraction. Since rainwater and dust enter the bellows from the outside through the ventilation hole, however, the sliding portion between the output cylinder and the output push rod gets rusted and spoiled.